1. Field of the Invention
The present invention relates to interpolation filters. In particular, the present invention relates to an interpolation filter for use of sending end of a wireless telecommunication system.
2. Description of the Related Art
For the wireless telecommunication system like CDMA-2000 (Code Division Multiple Access-2000), W-CDMA (Wideband-Code Division Multiple Access), or SDR (Software Defined Radio), a low complexity and a low power are essential factors. It is no wonder that so much research on those are actively under development right now. Among others, a pulse-shaping interpolation filter for a sending end of such system decreases the interference between symbols, and provides an appropriate shape for the frequency region. In fact, the standard set for the mobile telecommunication system like IS-95 (Industry Standard-95), CDMA-2000, W-CDMA and so forth, particularly requires use of a FIR (far infra-red) filter for the pulse-shaping interpolation filter. Recently, after further research for developing the interpolation with a low speed and low calculation work and low power, a structure based on look up table (LUT) has been introduced.
A typically used FIR transversal filter as suggested by Hogenauer requires an excessive amount of multiplication and a high-speed filtering. That is why the LUT filter based on the ROM (read only memory), or a new filter structure with ½ smaller LUT size and memory demand using the symmetry of the filter coefficient was introduced. Such filters have the structure of polyphase decomposition. Especially the FIR filter includes polyphase subfilters corresponding to the interpolation rate, and each subfilter conducts a low-speed parallel filtering that is proportional to the parallel process and the interpolation rate. Unfortunately however, the LUT filter based on the ROM occupies 90% of the entire filter region when the filter is actually implemented, so the memory demand thereof is consequently very high.